Ever since the invention of bicycles, there was a search for an easier and more comfortable propelling system, a system that will improve bicycles usability hence make them useful for a wider range of people as a daily transportation mean.
The common trend towards green transportation also encourages the use of man powered vehicles.
The first bicycles were merely supporting a running person's weight. Cranked propelling pedals, driving the front wheel were later added. A chain drive with the crank pedals driving the rear wheel followed. Manual gears were added for easier riding over hills. Those gears diverted from internal planetary gears assembled within the rear wheel hub to the external, more popular, chain gears. Motorizing bicycles formed a different branch spanning from motorcycles of all kinds to the electrically powered bicycles.
Gear shifting devices added, while widening the dynamic range of the engine, motor, and human propelled bicycles, require higher technical understanding to operate and take full use of their advantages.
The average potential rider does not have the skills or will to operate manual shifters and is usually baffled by the plurality of the gear ratios on one hand. On the other hand wants the convenience of automatic transmission which conceals the hassles and whistles of the underline mechanics.
With Motor-scooters the tendency is to implement a belt variators electronically controlled as the preferred transmission method. In man powered vehicles, we look for a better energy efficient mechanisms. Hence, variators, slip clutches, robotic clutches, or even computerized actuators utilized to operate common chain gear derailleur's, are a patched improvement to a non satisfactory solution.
Therefore, there is a long felt need for a drive that would eliminate the confusion of deciding, which is the suitable ratio required for a specific terrain, and provide a smooth, comfortable and easy ride.
Shimano, U.S. Pat. No. 3,513,726, discloses an automatic three-stage speed change bicycle hub, which comprises a driving sleeve having a usual driving sprocket wheel, a planetary gear mechanism provided between said driving sleeve and the hub shell, a high speed-ratio transmission ratchet gearing, both ratchet gearing being associated with said planetary gear mechanism, and centrifugal governor weights adapted to effect operative engagement and disengagement of said high speed-ratio transmission ratchet gearing according to speed of rotation of the driving sprocket wheel.
Lenoble, U.S. Pat. No. 5,976,052, discloses a compact automatic gear change device for a bicycle in which all of the sprocket wheels mesh by means of an intermediate moving element and are equipped with anti-reverse pawls automatically controlled by mechanical or electronic tachometers. The first disclosed device is a line gear cluster incorporated in a sealed housing and connecting the bottom bracket spindle to the wheel spindle by completely eliminating the drive chain. The second disclosed device is composed of coaxial sprocket wheels driven by three intermediate moving elements positioned on the inside, whereas the starting teeth of the wheels, the pawls and the tachometers are positioned on the outside. The assembly disclosed is housed in two sealed housings that rotate over one another.
The speed-ratio transmission of the gear sets as disclosed in the prior art is depend upon the angular velocity of the driving wheel, however these systems do not consider requirements or inputs of the driven wheel such as the rotated load or actual the angular velocity of the driven wheel.
Hadeev, WO/2008/147236, discloses a mechanisms which modifies the transmission ratio when the shaft load is modified. A mechanism which can be, for example, in the form of a tool reducing gear, in particular a screwdriver, a car clutch gear and a helicopter or gyrocopter propeller reducing gear. Hadeev transmission ratio converter designed in the form of a device comprising a planetary differential gear with a carrier and different-diameter toothed wheels, one of which is rigidly secured to an output shaft for transmitting the engine energy thereto, and the second toothed wheel is put onto the drive part of a friction device with a determined sliding force which produces a braking torque and an adjusting transmission ratio, the driven part of the friction device being rigidly connected to the third central toothed wheel which is freely rotatable on the output shaft and transmits rotation, via a reduction gear, to a fourth toothed wheel which is rigidly connected to the output shaft.
However, there is still a long felt need for a simple drive that can be applied for man powered devices such as bicycles. A drive that would determine the application of the power source onto the driven-wheel depended upon the angular velocity of the driven wheel which is carrying the rotated load. The device should be enclosed to conceal the underlining mechanism, maintenance free, and preferably an “add-on” to the existing fleet of bicycles.